The present invention relates to a metal complex having a xcex2-diketonate, a process for producing the same, a photoelectric conversion element, and a photochemical cell.
Inorganic semiconductors, such as a monocrystal, polycrystal, and amorphous silicon, are used as photoelectric conversion materials used for solar cells. These materials are pointed out to have the problems that they require large energy in a production process and contain components that are not environmentally preferable. To deal with these problems, an energy converter utilizing a photoelectric chemical reaction that takes place at the boundary between a photo-semiconductor and an electrolytic solution, has been developed. Titanium oxide used in the device is stable photoelectrochemically, and superior as an electrode material of a metal oxide semiconductor. However, titanium oxide has an inferior spectrum matching sunlight, and it is not expected to have high efficiency, because it has a bandgap as large as 3.0 eV.
Therefore, an organic dye is utilized to be adsorbed onto the surface of titanium oxide, to sensitize it. It is known that the adsorbed dye has a sensitizing effect, and that titanium dioxide which has a large specific surface area as the electrode of a photo-semiconductor, is used to improve the efficiency of utilization of light (JP-A-1-220380 (xe2x80x9cJP-Axe2x80x9d means unexamined published Japanese patent application.)). Also, it is known to use a thin film of titanium dioxide having micropores on the surface thereof (JP-A-8-99041). However, titanium dioxide has a large forbidden band and therefore cannot absorb light in the visible region. It is therefore necessary to coat titanium dioxide with a photosensitizer that absorbs light in a wavelength range in 300 to 2000 nm, to aim at sunlight, and an organic dye is used for this purpose.
As the organic dye, many compounds, such as xanthene-series dyes, cyanine-series dyes, basic dyes, porphyrin-series compounds, azo dyes, and Ru complexes, are known (JP-A-11-144772 and JP-T-7-500630 (xe2x80x9cJP-Txe2x80x9d means a publication of the translation of an international patent application.)). It has been considered that a solar cell, which is coated with an Ru complex and is sensitized with a dye, has a high photoelectric conversion efficiency, and that such the solar cell is produced at lower costs in contrast to even a silicon solar cell. Although these points are advantageous, the performance of a cell depends on a sensitizing dye, and it is desired to develop a high-performance dye upon developing a high-performance cell.
An object of the present invention is to provide a dye having high light absorbance over a wide wavelength range. Another object of the present invention is to provide a photoelectric conversion element using the dye. A further object of the present invention is to provide a photochemical cell using the element.
Other and further objects, features, and advantages of the invention will appear more fully from the following description, taken in connection with the accompanying drawings.
The inventors of the present invention, having made earnest studies on the above objects, developed a dye which is composed of a novel xcex2-diketonate metal complex and found that light in a wide wavelength range (less than 800 nm) can be absorbed by this dye, to complete the present invention.
Accordingly, according to the present invention the following inventions are provided.
(1) A metal complex having a xcex2-diketonate represented by the following formula (1): 
wherein M represents a metal atom of the VIII group; R1, R2 and R3 each represent a group or an atom select the group consisting of an alkyl group, an aryl gr hydroxyl group, an amino group, an alkoxy group, a hydrogen atom and a halogen atom; Xxe2x88x921 represents an ion selected from a halogen ion, a nitric acid ion, a sulfonic acid ion, a fluoroboric acid ion, a fluorophosphoric acid ion and a perchloric acid ion; and L1 or L2 respectively represents a 2,2xe2x80x2-bipyridine group or a 1,10-phenanthroline group, each of which may be substituted with a group or an atom selected from an alkyl group, a carboxyl group, a sulfonic acid group, a phosphonic acid group, a hydroxyl group, an amino group, a hydrogen atom and a halogen atom.
(2) A metal complex having a xcex2-diketonate represented by the following formula (2): 
wherein M represents a metal atom of the VIII group; R1, R2 and R3 each represent a group or an atom selected from the group consisting of an alkyl group, an aryl group, a hydroxyl group, an amino group, an alkoxy group, a hydrogen atom and a halogen atom; and L1 or L2 respectively represents a 2,2xe2x80x2-bipyridine group or a 1,10-phenanthroline group, in which one or both of L1 or L2 may be substituted with an acidic group selected from a carboxyl group, a sulfonic acid group, a phosphonic acid group and a hydroxyl group each of which is neutralized.
(3) A method for producing a metal complex having a xcex2-diketonate represented by the following formula (1), comprising heating a metal complex of the VIII group having, as a ligand, L1 L2 which represent a 2,2xe2x80x2-bipyridine group or a 1,10-phenanthroline group (these groups may be substituted with a group or an atom selected from an alkyl group, a carboxyl group, a sulfonic acid group, a phosphonic acid group, a hydroxyl group, an amino group, a hydrogen atom and a halogen atom), and a xcex2-diketone derivative, in the presence of an alkali and a solvent, and treating the resulting product with an aqueous solution containing an acid. 
(4) A method for producing a metal complex having a xcex2diketonate represented by the following formula (2), comprising adding an alkali to the aqueous solution containing the xcex2-diketonate described in the above item (3). 
(5) A photoelectric conversion element, which comprises a porous oxide semiconductor layer laminated on a layer composed of an electric conductor, and the metal complex as stated in the above item (1) or (2) adsorbed to the porous oxide semiconductor layer.
(6) A photochemical cell, which comprises the photoelectric conversion element as stated in the above item (5), a counter electrode, and a charge-transfer layer.